Updated

Police killed 13 suspected gang members Monday in a shootout in South America's largest city, as authorities foiled a plot to attack prison guards just six weeks after an unprecedented week of violence that killed almost 200 people.

The presumed members of the First Capital Command gang — 12 men and one woman — were killed in a gunfight with police outside a prison in the industrial suburb of Sao Bernardo do Campo, said district police chief Marco Antonio de Paula Santos.

The gang's plan was to shoot as many as 60 guards from four lockups over a 10-day period as they headed to work or finished their shifts, Santos said. But officers learned about it by listening in on gang leaders' phone calls and from informants, according to Santos and state police.

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Before dawn Monday, undercover officers saw what Santos called suspicious activity as three guards were leaving the Sao Bernardo prison, and police exchanged gunfire with the suspects.

"We decided not to let them open fire on the guards," Santos said.

Some suspects were killed just outside the prison, and the rest were shot dead in gunbattles on the streets as they tried to flee in cars, Santos said. One officer was grazed by a bullet, five suspects were taken into custody uninjured and at least four escaped. Authorities seized four revolvers, four pistols and a rifle.

The violence came just six weeks after imprisoned gang leaders allegedly ordered attacks against police across the city and Sao Paulo state, sparking a weeklong wave of violence that killed nearly 200 police, prison guards, suspected criminals and jail inmates.

Last month's attacks terrified Sao Paulo, prompting businesses to shut down and parents to pull their children from schools after suspected gang members torched scores of buses and attacked other symbols of authority across the region.

Jailed members of the gang allegedly ordered the rampage using smuggled cellular phones because of outrage over a government plan to transfer gang leaders to more secure prisons. The May 12-19 spree left 41 officers and prison guards dead.

Police struck back, killing 123 people, many described as gang members, though human rights advocates said they suspected innocents were killed. Twenty-three inmates also died in prison rebellions.

There were no signs that Monday's violence was spreading or having any impact on daily life in Sao Paulo, a metropolis of 18 million.

"We thought this might happen, and unfortunately, it did," Sao Paulo state Gov. Claudio Lembo told Jovem Pan radio.

Police were on high alert, but Lembo said the city was calm.

"The situation is of complete tranquility, there are no problems in Sao Paulo," Lembo said.